In many combustion-based systems including, for example, turbine engines, fuel can be mixed with another fluid, such as air, prior to being delivered to and burned in a combustion area. Several problems can arise when introducing fuel to the flow path of a fluid upstream of a combustion area.
One known system 10 for introducing fuel to an air flow in a turbine engine is shown in FIG. 1. Air 12 from the compressor flows along a surface 14 of a turbine engine combustor component 16. A portion or layer of the air 12 that is at and in the immediate vicinity of the surface 14 is referred to as the boundary layer 18. The air flow 12 has an associated velocity profile 20. The velocity of the air 12 at the boundary layer 18 approaches substantially zero.
As shown, fuel 22 can be introduced to the air flow 12 at or near the boundary layer 18 by a fuel injector 24. Downstream of the fuel injector 24 is a combustion area 26, which can be, for instance, a transition duct. After the fuel 22 is introduced to the air flow 12, it can travel downstream with the rest of the air flow 12. Experience has shown that concentrations of the fuel 22 remain on the boundary layer 18 of air 12, and such fuel 22 moves at relatively low velocities. Consequently, there is an increased risk that flames from the combustion area 26 will be able to travel upstream through such low velocity fuel 22. If it travels far enough upstream, the flame can be held at the fuel injector 24 due to the continuing supply of fuel 22, which can result in significant and expensive damage to the injector 24 and the component 16.
Some of the existing fuel injection systems attempt to avoid the low velocity profile of the boundary layer 18. One such system 30 is shown in FIG. 2. As shown, a fuel injector 24 projects into the flow path 12 and beyond the boundary layer 18. Thus, when the fuel 22 is introduced to the air flow 12, the fuel 22 does not remain on the boundary layer 18. An example of such a system in a turbine engine is shown in FIG. 3. The combustor section 32 of a turbine engine can include a head end 34. As air 12 from the compressor enters the head-end 34, fuel can be injected into the air flow 12 by a fuel ring 36, which is sometimes referred to as the C-stage. The fuel ring 36 is positioned within the air flow path 12 and away from the boundary layer.
While the systems shown in FIGS. 2 and 3 can minimize the possibility of flame holding, the fuel injectors 24 and/or the fuel ring 36 can fail due to excitations, such as flow induced vibration, combustion dynamics, etc. In addition, placement of the fuel injectors 24 and/or the fuel ring 36 in the flow path 12 can interfere with the aerodynamics of the flow 12 and can cause a drop in the pressure of the air flow 12.
Thus, there is a need for a system for introducing fuel to a flow path that can minimize flame holding potential while avoiding substantial intrusion into the flow path.